The invention concerns a pneumatic door operating device having an electro-pneumatic control, particularly suited for doors of vehicles used in public transportation.
Door operating devices are generally controlled pneumatically or electro-pneumatically, meaning that the driver releases a pneumatic or electrical impulse to open or close the door. This impulse, which travels over a control valve, also called a door valve, and actuates a door control cylinder, also called a door operator, with forced air, whereby the movements of the door cylinder piston effect the opening and closing movements of the door.
In such a system, it is generally required that the closing movements of a pneumatically operable vehicle door automatically convert to an opening movement when persons or objects become wedged in a closing door. Furthermore, the requirement exists that after the emergency valve has been activated and then reset for normal operation, no undesired door movements are present. A well-known pneumatic door operating device which meets the requirements has an emergency valve arrangement which consists of a valve combination of three 3/2 routing valves, namely, two magnet servo-valves and a pneumatic control valve. The door valve, which has been built into this unit, consists of a magnetically controlled 4/2 routing valve.
The object of the invention is to realize the described safety measures using fewer expensive valve devices.